octeontx2-vf: Ethtool support

Added ethtool support for VF devices for
 - Driver stats, Tx/Rx perqueue stats
 - Set/show Rx/Tx queue count
 - Set/show Rx/Tx ring sizes
 - Set/show IRQ coalescing parameters
 - RSS configuration etc

It's the PF which owns the interface, hence VF
cannot display underlying CGX interface stats.
Except for this rest ethtool support reuses PF's
APIs.

Signed-off-by: Tomasz Duszynski <tduszynski@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>